Unilateral common carotid artery occlusion in gerbils produced a decreased level of 5-HT and accumulation of 5-HIAA in the ischemic cerebral cortex. The reduction of 5-HT was aggravated by pretreatment with PCPA the inhibitor of tryptophan hydroxylase and pargyline the inhibitor of monoamine oxidase suggestive of decreased 5-HT synthesis and degradation, respectively, occurring in ischemia. Moreover the inhibition of 5-HIAA out-transport from brain was indicated by the more pronounced accumulation of 5-HIAA probenecid pretreated ischemia than the ischemic animals which 5--HT levels were low in the cerebral cortex. This project is completed. BIBLIOGRAPHIC REFERENCES: Mrsulja, B.B., Mrsulja, B.J., Spatz, M. and Klatzo, I.: Brain serotonin after experimental vascular occlusion. Neurology 26: 785-787, 1976. Mrsulja, B.B., Mrsulja, B.J., Spatz, M. and Klatzo, I.: Monoamines in cerebral ischemia in relation to brain edema. In: Dynamics of Brain Edema, Pappius, H.M., and Feindel, W. (Eds). Berlin Heidelberg, Springer-Verlag, 1976, pp. 187-192.